Color processing apparatus, color processing method, non-transitory computer-readable storage medium

ABSTRACT

An input chromaticity data calculation unit 113 calculates input chromaticity data rg from device-dependent color data RGB. A chromaticity data transformation unit 114 transforms the input chromaticity data rg into output chromaticity data xy by referring to an LUT stored by an LUT storage unit 13. A total amount calculation unit 115 refers to the LUT of the LUT storage unit 13 to calculate a total amount Σ′XYZ of the device-independent color data XYZ from the color data RGB. An output color data calculation unit 116 uses the total amount Σ′XYZ to calculate color data XYZ from the output chromaticity data xy.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to color transformation processing ofimage data input from an image input device.

Description of the Related Art

Spectral sensitivity characteristics of an image input device astypified by a digital camera commonly do not match visual spectralcharacteristics (a color matching function) of a person. An RGB value ofimage data acquired by an image input device is a value that depends oncharacteristics of the image input device. Therefore, it is necessary totransform an RGB value that is a device-dependent color signal(hereinafter referred to as a device RGB value) into tristimulus values(XYZ values) that are device-independent color signals or a standard RGBvalue such as in an sRGB space or an AdobeRGB space.

A method for transforming a device RGB value into tristimulus values bya matrix operation is known, but by matrix operation processing atransformation having high precision high chroma color in particular isnot achieved, and a color transformation precision decreases.Accordingly, the International Publication 2013/101639 discloses aninvention that performs high precision color transformation processingin the entire region of visible light by performing a transformationfrom a device RGB value to an XYZ value by a lookup table (LUT)computation instead of a matrix operation.

In the invention of International Publication 2013/101639, to generatean LUT used in the color transformation, grid partitioning is performedfor the entirety of a visible light range, and spectral data thatcorresponds to each grid point is generated. Subsequently, a device RGBvalue and an XYZ value corresponding to the spectral data of each gridpoint is calculated, and an LUT indicating a correspondence betweendevice RGB values and XYZ values is formed. This LUT has atwo-dimensional input/output format, and the invention of theInternational Publication 2013/101639 transforms three-dimensional colorinformation (RGB values) into two-dimensional chromaticity informationp=R/(R+G+B), q=G/(R+G+B), and inputs the chromaticity information pqinto the LUT to obtain two-dimensional xy chromaticity data. The xychromaticity data is then used to calculate tristimulus values (XYZvalues).

To transform xy chromaticity data to XYZ values, conventionally there isa necessity for a value calculated by (X+Y+Z) as a transformationcoefficient. Because the invention of the International Publication2013/101639 uses a value calculated by (R+G+B) as an alternative for atransformation coefficient to calculate the XYZ values, it cannot besaid that calculation precision of the XYZ values is high.

SUMMARY OF THE INVENTION

The present invention provides a technique for realizing improvement ofcolor reproducibility precision when transforming device-dependent colordata into chromaticity data, and then transforming it todevice-independent color data.

According to the first aspect of the present invention, there isprovided a color processing apparatus comprising: a first calculationunit configured to calculate first chromaticity data fromdevice-dependent color data; a transformation unit configured totransform the first chromaticity data into second chromaticity data byreferring to a table; a second calculation unit configured to calculatea total amount of device-independent color data from thedevice-dependent color data by referring to the table; and a thirdcalculation unit configured to use the total amount to calculate thedevice-independent color data from the second chromaticity data.

According to the second aspect of the present invention, there isprovided a color processing method, comprising: calculating firstchromaticity data from device-dependent color data; transforming thefirst chromaticity data into second chromaticity data by referring to atable; calculating a total amount of device-independent color data fromthe device-dependent color data by referring to the table; and using thetotal amount to calculate the device-independent color data from thesecond chromaticity data.

According to the third aspect of the present invention, there isprovided a non-transitory computer-readable storage medium storing aprogram for causing a computer to function as a first calculation unitconfigured to calculate first chromaticity data from device-dependentcolor data; a transformation unit configured to transform the firstchromaticity data into second chromaticity data by referring to a table;a second calculation unit configured to calculate a total amount ofdevice-independent color data from the device-dependent color data byreferring to the table; and a third calculation unit configured to usethe total amount to calculate the device-independent color data from thesecond chromaticity data.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a processing configurationexample of a color processing apparatus of a first embodiment.

FIG. 2 is a flowchart for describing color transformation processing inthe color processing apparatus.

FIGS. 3A-3D are views illustrating spectral distribution in a case whentwo parameters λ1 and λ2 are caused to change.

FIGS. 4A and 4B are views illustrating an example of a correspondencerelationship between rg chromaticity data and xy chromaticity data in anentire region of a visible range.

FIG. 5 is a block diagram illustrating a processing configurationexample of a color processing apparatus of a second embodiment.

FIG. 6 is a flowchart for describing color transformation processing ofthe second embodiment.

FIG. 7 is a block diagram illustrating an example of a hardwareconfiguration of the color processing apparatus.

DESCRIPTION OF THE EMBODIMENTS

Below, explanation is given in detail with reference to the figures ofan image processing apparatus (a color processing apparatus) and animage processing method (a color processing method) of embodimentsaccording to the present invention. Note that these embodiments do notlimit the present invention according to the scope of the claims, andnot all of the combinations of configurations described in theembodiments are necessarily required with respect to the means to solvethe problems according to the present invention.

[First Embodiment]

[Device Configuration]

The block diagram of FIG. 1 illustrates an example of a processingconfiguration of a color processing apparatus 11 of the firstembodiment. The color processing apparatus 11 performs colortransformation processing of image data input from an image acquisitionapparatus 12 based on a lookup table (LUT) stored by an LUT storage unit13, and stores image data obtained by the color transformationprocessing in a storage device 14, for example.

In the color processing apparatus 11, an input unit 111 is input withimage data (RGB data) from the image acquisition apparatus 12, which isan image input device such as a digital camera or a scanner. An inputcolor data acquisition unit 112 acquires device-dependentthree-dimensional color data (hereinafter referred to as the input colordata) for each pixel of the input image data. An input chromaticity datacalculation unit 113 calculates two-dimensional chromaticity data(hereinafter referred to as the input chromaticity data) from the inputcolor data. A chromaticity data transformation unit 114 transforms theinput chromaticity data into output chromaticity data based on an LUTstored by the LUT storage unit 13.

A total amount calculation unit 115 calculates, based on the input colordata, a total amount of output data (hereinafter referred to as anoutput total amount) that is described later. An output color datacalculation unit 116 uses the output chromaticity data and the outputtotal amount to calculate device-independent output color data. Anoutput unit 117 stores image data based on the output color data(hereinafter referred to as output image data) in the storage device 14,for example.

The block diagram of FIG. 7 illustrates an example of a hardwareconfiguration of the color processing apparatus 11. A microprocessor(CPU) 201 realizes the processing configuration illustrated in FIG. 1 byexecuting a program stored in the storage unit 203 with a random accessmemory (RAM) 202 as a work memory. The storage unit 203 is configured bya read only memory (ROM), a flash memory, or the like, and stores anoperating system (OS), a program for realizing the processingconfiguration, or the like.

A media interface 204 is, for example, a serial bus interface for USB orthe like, a memory card host controller, or the like, and is used toconnect to the LUT storage unit 13 which is provided as a USB memory ora memory card. An input interface 205 is an interface such as for, forexample, USB, SATA, PCIe, SDI, MIPI (registered trademark) or the like,and is used for input of image data from the image acquisition apparatus12 which is a digital camera, a scanner, or the like.

An output interface 206 is an interface for USB, SATA, a memory cardhost controller, or the like. The output interface 206 is used foroutput of image data to the storage device 14 which is a storage mediumsuch as a hard disk drive (HDD), a solid state drive (SSD), USB memory,or a memory card. A CPU 201 controls each interface via a system bus207, and performs input and output of image data and referencing of theLUT.

Note that the LUT storage unit 13 and the storage device 14 may beprovided together. In addition, it is possible to use a wired orwireless network for connections between the color processing apparatus11, the image acquisition apparatus 12, the LUT storage unit 13, and thestorage device 14. In a case of using a network, the LUT storage unit 13and the storage device 14 may be provided as server apparatuses on thenetwork. In addition, in a case of using a monitor in place of thestorage device 14 as an output destination of the output unit 117, it ispossible to use SDI, HDMI (registered trademark), DisplayPort or thelike as the output interface 206.

[Color Transformation Processing]

By the flowchart of FIG. 2, description is given of color transformationprocessing in the color processing apparatus 11. The input unit 111 isinput with image data from the image acquisition apparatus 12 (stepS21). The input color data acquisition unit 112 acquiresthree-dimensional color data RGB for each pixel of the input image dataas the input color data (step S22).

Next, the input chromaticity data calculation unit 113 calculates inputchromaticity data rg from the input color data by the followingequations, as input chromaticity data (step S23).r=R/(R+G+B);g=G/(R+G+B);  (1)

Next, the chromaticity data transformation unit 114 transforms the inputchromaticity data rg to output chromaticity data xy by a calculation ofthe output chromaticity data xy from the input chromaticity data rg thatuses an interpolation calculation that refers to the LUT stored in theLUT storage unit 13 (step S24). In other words, the output chromaticitydata xy that corresponds to the input chromaticity data rg is stored inthe LUT. Although detail is described later, the total amountcalculation unit 115 calculates an output total amount Σ′_(XYZ) from theinput color data RGB, based on the input chromaticity data rg (stepS25).

Next, the output color data calculation unit 116 uses the outputchromaticity data xy and the output total amount Σ′_(XYZ) to calculateoutput color data XYZ by the following equations (step S26).X=xΣ′_(XYZ);Y=yΣ′_(XYZ);Z=(1−x−y)Σ′_(XYZ);  (2)

Next, the output unit 117 stores output image data (the XYZ data)generated based on the output color data XYZ in the storage device 14for example (step S27).

[LUT Generation]

Expressing a rectangular shape that indicates spectral distribution bytwo parameters is considered. Assuming that spectral radiance changesfrom 0 to 1 in a wavelength λ1 and spectral radiance changes from 1 to 0in a wavelength λ2, it is possible to express any spectral distributionby two parameters (the wavelengths λ1 and λ2).

FIGS. 3A-3D are views illustrating spectral distribution in a case whentwo parameters λ1 and λ2 are caused to change. If λ1<λ2, spectraldistribution of a bandpass shape as illustrated in FIGS. 3A and 3B isachieved, and if λ1>λ2, spectral distribution of a band eliminationshape as illustrated in FIGS. 3C and 3D is achieved. Spectral datahaving the shapes illustrated in FIGS. 3A-3D is hereinafter referred toas “rectangular spectral data”. It is possible to express rectangularspectral data I_(λ1λ2)(λ) by the following formula.if (λ1<λ2){if (λ1≤λ≤λ2)I _(λ1λ2)(λ)=1;elseI _(λ1λ2)(λ)=0;}if (λ1≥λ2){if (λ2<λ<λ1)I _(λ1λ2)(λ)=0;elseI _(λ1λ2)(λ)=1;}  (3)

Tristimulus values X_(λ1λ2), Y_(λ1λ2), Z_(λ1λ2) of the rectangularspectral data I_(λ1λ2)(λ) are calculated by the following equations.X _(λ1λ2) =k∫ _(vis) I _(λ1λ2)(λ)x(λ)dλ;Y _(λ1λ2) =k∫ _(vis) I _(λ1λ2)(λ)y(λ)dλ;Z _(λ1λ2) =k∫ _(vis) I _(λ1λ2)(λ)z(λ)dλ;  (4)

Here ∫_(vis)dλ is the integral of the visible wavelength range,k=100/∫_(vis) y(λ)dλ, and

x(λ)y(λ)z(λ) is a color matching function.

In addition, output values R_(λ1λ2), G_(λ1λ2), B_(λ1λ2) of an imagecapturing device in a case of acquiring the rectangular spectral dataI_(λ1λ2)(λ) by the image acquisition apparatus 12 are calculated by thefollowing equations.R _(λ1λ2)=∫_(vis) I _(λ1λ2)(λ)r(λ)dλ;G _(λ1λ2)=∫_(vis) I _(λ1λ2)(λ)g(λ)dλ;B _(λ1λ2)=∫_(vis) I _(λ1λ2)(λ)b(λ)dλ  (5)

Here, r(λ)g(λ)b(λ) is the spectral sensitivity characteristics of theimage capturing device.

The RGB values R_(λ1λ2), G_(λ1λ2), B_(λ1λ2) calculated by Equations (5)are transformed into the rg chromaticity data r_(λ1λ2), g_(λ1λ2) byusing Equations (1). Furthermore, the XYZ values X_(λ1λ2), Y_(λ1λ2),Z_(λ1λ2) calculated by Equations (4) are transformed into xychromaticity data x_(λ1λ2), Y_(λ1λ2) by using the following equations.x _(λ1λ2) =x _(λ1λ2)/(x _(λ1λ2) +y _(λ1λ2) +z _(λ1λ2))y _(λ1λ2)=_(λ1λ2)/(x _(λ1λ2) +y _(λ1λ2) +z _(λ1λ2));  (6)

The rg chromaticity data r_(λ1λ2), g_(λ1λ2) and the xy chromaticity dataX_(λ1λ2), y_(λ1λ2) obtained in this way is stored in an LUT as acorrespondence relationship between xy chromaticity data (output) and rgchromaticity data (input) corresponding to the rectangular spectral dataI_(λ1λ2)(λ). In such a case, by causing the two parameters (λ1, λ2) tochange at equal intervals (for example, at 5 nm intervals) and causingcharacteristics of the rectangular spectral data I_(λ1λ2)(λ) to change,the correspondence relationship for the rg chromaticity data and the xychromaticity data of the entire visible range is obtained.

FIGS. 4A and 4B are views illustrating an example of a correspondencerelationship between rg chromaticity data (FIG. 4A) and xy chromaticitydata (FIG. 4B) in an entire region of a visible range. If an LUT thatstores the correspondence relationship illustrated in FIGS. 4A and 4B isused, by an interpolation calculation that refers to the LUT, acalculation of output chromaticity data xy corresponding to any inputchromaticity data rg becomes possible.

[Output Total Amount Calculation]

To transform xy chromaticity data into tristimulus values XYZ, thetransformation of the following equations become necessary.X=xΣ _(XYZ) =x(X+Y+Z);Y=yΣ _(XYZ) ==y(X+Y+Z);Z=zΣ _(XYZ)=(1−x−y)(X+Y+Z);  (7)

For the invention of the International Publication 2013/101639, becausethe XYZ value is unknown, the output total amount Σ_(XYZ)=(X+Y+Z) isalso unknown. Accordingly, as an alternative to the output total amountΣ_(XYZ), a value calculated by Σ_(RGB)=(R+G+B) is used as atransformation coefficient (hereinafter referred to as an input totalamount) to calculate the XYZ value by the following equations.X=xΣ_(RGB);Y=yΣ_(RGB);Z=(1−x−y)Σ_(RGB);  (8)

If the spectral sensitivity characteristics of the image capturingdevice of the image acquisition apparatus 12 satisfy a router condition(r(λ)g(λ)b(λ)=x(λ)y(λ)z(λ)), Σ_(XYZ)=Σ_(RGB) is achieved, and accuratetristimulus values are calculated. However, if spectral sensitivitycharacteristics of a typical image capturing device do not satisfy therouter condition, Σ_(XYZ)≠Σ_(RGB), as a result, an error occurs in thetristimulus values calculated.

Accordingly, in this embodiment, an output total amount Σ′_(XYZ) iscalculated by performing a correction according to a correctioncoefficient gain illustrated in the following equation to an input totalvalue Σ_(RGB).Σ_(XYZ)=gain·Σ_(RGB)  (9)

By the correction, Σ′_(XYZ)≈Σ_(XYZ), and it becomes possible to performat high precision a transformation of the xy chromaticity data to thetristimulus values XYZ. To perform the correction according to Equation(9), when generating the LUT, the correction coefficient gain iscalculated by the following Equations from the relationship between Xm,Ym, and Zm values obtained by measuring a certain color by using acolorimeter or the like, and Rm, Gm, and Bm values output by the imageacquisition apparatus 12 with respect to the same color.gain=(Xm+Ym+Zm)/(Rm+Gm+Bm);r=Rm/(Rm+Gm+Bm);g=Gm/(Rm+Gm+Bm);  (10)

In other words, the correction coefficient gain indicates a ratiobetween device-dependent color data RGB and device-independent colordata XYZ, with respect to the same color. By adding an output value ofan LUT that associates the correction coefficient gain and the rgchromaticity data, expansion is made to an LUT with two element inputs rand g, and three outputs: x, y, and gain. By this, it becomes possibleto acquire the correction coefficient gain with respect to the inputchromaticity data rg. Note, if the input chromaticity data rg and the rgchromaticity data stored in the LUT do not match, calculating thecorrection coefficient gain that corresponds to the input chromaticitydata rg by the interpolation calculation is a matter of course.

A method of calculating the output total amount Σ′_(XYZ) is not limitedto the multiplication of the input total amount Σ_(RGB) and thecorrection coefficient gain illustrated in Equation (9). For example, amethod of calculating by a linear sum of RGB values illustrated inEquation (11) may be used, and a method of calculating by a polynomialexpression that uses non-linear values illustrated in Equation (12) maybe used.Σ′_(XYZ) =aR+bG+cB+d;  (11)Σ′_(XYZ) =aR ² bG ² cB ² +dR+eG+fB+gRG+hGB+iBR+j  (12)

Note that, in Equations (11) and (12), coefficients a-d or coefficientsa-j are added to output values of the LUT associated with the rgchromaticity data. In other words, in comparison to the transformationcoefficient Σ′_(RGB), it is sufficient if there is a correction methodsuch that Σ′_(XYZ) which is a correction result approaches (X+Y+Z), andthe correction method is not limited.

[Output Color Data Calculation Unit]

As is clear from the aforementioned description, the output color datacalculation unit 116 calculated the tristimulus values XYZ from theoutput chromaticity data xy by the following equations.X=xΣ′ _(XYZ) =x·gain·Σ_(RGB);Y=yΣ′ _(XYZ) =y·gain·Σ_(RGB);Z=(1−x−y)Σ′_(XYZ)=(1−x−y)·gain·Σ_(RGB);   (13)

In this way, a two-dimensional LUT is used to calculate the chromaticitydata xy from the chromaticity data rg, and calculate the tristimulusvalues XYZ from the chromaticity data xy. In such a case, by usingΣ′_(XYZ), which is the result of correcting Σ_(RGB), as thetransformation coefficient Σ_(XYZ) for transforming xy values into XYZvalues, calculating precision of the XYZ values, specifically the colorreproducibility precision, improves.

[Second Embodiment]

Below, description is given in detail of an image processing apparatus(a color processing apparatus) and an image processing method (a colorprocessing method) of the second embodiment according to the presentinvention. Note that in the second embodiment, there are cases in whichthe same reference numerals are added and detailed description isomitted for configurations approximately the same as those in the firstembodiment. In the second embodiment, description is given of an exampleof adding to the color transformation processing described in the firstembodiment a function for determining the existence or absence ofinformation necessary for calculation of the output total amountΣ′_(XYZ), and controlling the color transformation processing based onthe determination result.

The block diagram of FIG. 5 illustrates an example of a processingconfiguration of the color processing apparatus 11 of the secondembodiment. The configuration of the color processing apparatus 11illustrated in FIG. 5 comprises, in addition to the processingconfiguration illustrated in FIG. 1, a determination unit 121 fordetermining whether an LUT stored by the LUT storage unit 13 includesinformation necessary for calculation of the output total amountΣ′_(XYZ).

By the flowchart of FIG. 6, description is given of color transformationprocessing of the second embodiment. Processing of step S21 to step S24is similar to that in the first embodiment. Next, the determination unit121 determines whether the information (for example the correctioncoefficient gain) necessary for the calculation of the output totalamount Σ′_(XYZ) is included in an LUT stored by the LUT storage unit 13(step S31). If the LUT includes this information, the processingproceeds to step S25, and the total amount calculation unit 115calculates the output total amount Σ′_(XYZ) similarly to in the firstembodiment.

Meanwhile, if information necessary for calculation of the output totalamount Σ′_(XYZ) is not included in the LUT, the total amount calculationunit 115 calculates the input total amount Σ_(RGB) as the output totalamount Σ′_(XYZ) (step S32). Subsequently, similar to in the firstembodiment, calculation of the output color data XYZ that uses theoutput total amount Σ′_(XYZ) and the output chromaticity data xy by theoutput color data calculation unit 116 (step S26) and storing of outputimage data by the output unit 117 (step S27) are performed.

In this way, it becomes possible to perform color transformationprocessing similar that in the first embodiment only when informationnecessary for calculation of the output total amount Σ′_(XYZ) isobtained, and perform color transformation processing similar to theconventional technique in a case of using an LUT that has not beenprovided with this information.

[Variation]

The output color data was described as XYZ values above, but there is nolimitation to this, and, for example, RGB values of a color spacedefined by sRGB, AdobeRGB, or the like, or values such as CIELAB,CIELuv, or CIECAM02 may be used for the output color data. In addition,configuration may be taken to set the output color data as XYZ valuesand subsequently, by a typical definition expression, an ICC profile, orthe like, transform the XYZ values into RGB values defined by a standardcolor space or into values such as CIELAB, CIELuv, or CIECAM02, andoutput the values as the output image data. In other words, it ispossible to apply the present invention in the case of colortransformation processing for performing a transformation todevice-independent color data after transforming device-dependent RGBvalues into chromaticity data.

Other Embodiments

Embodiment(s) of the present invention can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2016-023979, filed Feb. 10, 2016, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A color processing apparatus comprising: a firstcalculation unit configured to calculate first chromaticity data fromdevice-dependent color data; a transformation unit configured totransform the first chromaticity data into second chromaticity data byreferring to a table; a second calculation unit configured to calculatea total amount of device-independent color data from thedevice-dependent color data by referring to the table, wherein the totalamount of device-independent color data is calculated in accordance witha multiplication of a correction coefficient corresponding to the firstchromaticity data that is stored in the table, and a sum total of thedevice-dependent color data; and a third calculation unit configured touse the total amount to calculate the device-independent color data fromthe second chromaticity data.
 2. The color processing apparatusaccording to claim 1, wherein the correction coefficient corresponds toa ratio between a sum total of the device-dependent color data and a sumtotal of the device-independent color data, with respect to the samecolor.
 3. The color processing apparatus according to claim 1, whereinthe table is a two-element input, three output table storing thecorrection coefficient and the second chromaticity data corresponding tothe first chromaticity data.
 4. The color processing apparatus accordingto claim 1, wherein, if information necessary for calculation of thetotal amount is not stored in the table, the second calculation unitoutputs the sum total of the device-dependent color data as the totalamount.
 5. The color processing apparatus according to claim 1, furthercomprising an input unit configured to input the device-independentcolor data from an image input device.
 6. The color processing apparatusaccording to claim 1, further comprising an output unit configured tooutput the device-independent color data to a storage device.
 7. Thecolor processing apparatus according to claim 1, wherein thedevice-dependent color data is three-dimensional RGB data, the firstchromaticity data is two-dimensional rg chromaticity data, the secondchromaticity data is two-dimensional xy chromaticity data, and thedevice-independent color data is three-dimensional XYZ data.
 8. A colorprocessing method, comprising: calculating first chromaticity data fromdevice-dependent color data; transforming the first chromaticity datainto second chromaticity data by referring to a table; calculating atotal amount of device-independent color data from the device-dependentcolor data by referring to the table, wherein the total amount ofdevice-independent color data is calculated in accordance with amultiplication of a correction coefficient corresponding to the firstchromaticity data that is stored in the table, and a sum total of thedevice-dependent color data; and using the total amount to calculate thedevice-independent color data from the second chromaticity data.
 9. Anon-transitory computer-readable storage medium storing a program forcausing a computer to function as a first calculation unit configured tocalculate first chromaticity data from device-dependent color data; atransformation unit configured to transform the first chromaticity datainto second chromaticity data by referring to a table; a secondcalculation unit configured to calculate a total amount ofdevice-independent color data from the device-dependent color data byreferring to the table, wherein the total amount of device-independentcolor data is calculated in accordance with a multiplication of acorrection coefficient corresponding to the first chromaticity data thatis stored in the table, and a sum total of the device-dependent colordata; and a third calculation unit configured to use the total amount tocalculate the device-independent color data from the second chromaticitydata.